I have got hold of a midi (USB) audio keyboard which was second hand. Windows detects the thing as an input device just fine and as far as I can tell it works.

Now here is the not so funny problem, I can't seem to find any software that allows me to use this wonderful input device to generate sounds.

I am not too fussy, but I would ideally like to use the thing as if it was a stand alone keyboard (different types of sounds etc) and if the software was free that would be good but then again I wouldn't mind paying a fee if it did what I wanted.

There is an overwhelming amount of MIDI software available for Windows, as the virtualization of the music production industry has really been rapidly progressing over the past few years.

A MIDI sequencer is typically what is used to sequence notes into a song. The biggest and best include: Cakewalk SONAR, Steinberg Nuendo and Cubase SX, Ableton Live, and Magix Samplitude. There are many variations of these applications based on your level of
need, and the prices range between less than $100 and over $1000. For example, Cakewalk's Kinetic retails at around $100 or less, but it offers only a tiny fraction of SONAR's capabilities.

Recently, powerful "budget" sequencers have been popping up as well, such as Mackie's Tracktion.

Free, basic MIDI sequencer or host applications also exist, and you could probably write your own if you studied the audio and MIDI portions of DirectX.

All of this said, MIDI by itself is just data, and you need a synthesizer to turn the data into audio that you can hear. Of course, Windows comes with a very generic MIDI synthesizer, but the trend in audio software is to use so-called "soft synths", or virtual
instruments, to produce audio from incoming MIDI messages.

These virtual instruments come in the form of plug-ins for the aforementioned sequencer host applications, and the sheer number available on the market today is mind-boggling. Many of these plug-ins are extremely high-quality, making your simple MIDI keyboard
sound like a real Boesendorfer piano, for example.

The definitive site for learning about soft synths and downloading free or trial versions is:

However, I highly recommend checking out the demo versions of the other MIDI sequencers mentioned earlier. The Cakewalk applications are all very good and play well with Windows (in particular, Project5 v2 is very easy to use and comes with great sound libraries)
and have very helpful support forums, although you might also want to demo Tracktion since it is aimed at making things easy for beginners.

Just a word of caution, though: once you get into computer-based music production, you'll soon discover that there is so much to learn, and it could end up stealing away your time from coding. Consider yourself warned!

You have misunderstood. I do not want a sequencer. I want a software backend for the audio keyboard. At the moment when I push a key literally nothing happens. It sends an electronic signal to the computer, and the computer ignores it
because it has no instructions. I am looking for a piece of software to turn that into an auditable sound ideally a piano.

I had a quick look though a great deal of the sites you listed and they appear to be directed at ordering various types of audio samples in order to create new music, not what I was after.

Re-SamIAm: I couldn't find much (anything?) while googling for TB303 emulators; and Hammerhead was a drum machine which is fine for some but not exactly what I was after (Piano etc) I am not sure what exactly USB synths are... so....

You have misunderstood. I do not want a sequencer. I want a software backend for the audio keyboard. At the moment when I push a key literally nothing happens. It sends an electronic signal to the computer, and the computer ignores it
because it has no instructions. I am looking for a piece of software to turn that into an auditable sound ideally a piano.

I had a quick look though a great deal of the sites you listed and they appear to be directed at ordering various types of audio samples in order to create new music, not what I was after.

Re-SamIAm: I couldn't find much (anything?) while googling for TB303 emulators; and Hammerhead was a drum machine which is fine for some but not exactly what I was after (Piano etc) I am not sure what exactly USB synths are... so....

You could always write your own The MIDI APIs are documented Look for midiInOpen, I believe...

You have misunderstood. I do not want a sequencer. I want a software backend for the audio keyboard.

You must have missed it in my post. MiniHost is a lightweight, standalone host for virtual instruments (i.e., it is not a sequencer). You would also need to download a virtual instrument to load into MiniHost, and that is why I recommended the KvR Audio site.

Most sequencing software will take input from MIDI and in fact, the 'game port' on your PC was, at one time, used as a midi IN port. Roland made a toy sampler called the tb303 that ended up causing the techno/noise/dance/rave revolution that appeared
in the 90s, and there used to be a bunch of emulators for it. If you want a classic example of it's sound, look for Josh Winx's "Higher State of Consciousness". It's an entire song generated around analog harmonic resolution. It's a neat sound but it got
overused and is kind of passe now.

Alas, they all seem to have disappeared. You can look for gigasampler if you want sampling and/or look for novation, roland, yamaha, moog synthesizer emulations as well. You aren't probably going to find an outright software synth created from scratch because
they all want to emulate the analog/old-skool digital sound of synths that came out years ago. The only other option is samplers.

That said, any sequencing software will give you the ability to input events from a keyboard. Plus, they usually have a vast array of sounds that will fire based off of those events. The sounds that happen aren't dependent on the synth that you use, but,
in fact, they can be changed.

MIDI in it's simplest is nothing more than a stream of note-on and note-off messages that are received and processed faster than your ears can perceive the lag.